Subsea connection apparatus

ABSTRACT

Apparatus for connecting a conduit to a subsea structure includes a frame connectable to the subsea structure by a docking mechanism, a conduit handling mechanism on the frame to facilitate positioning of the conduit for attachment to the subsea structure and a second docking mechanism for attaching a mobile manipulating device to the frame. In use, the mobile manipulating device connects to the conduit by means of a pull-in rope on a winch, and travels under its own power to the subsea structure while paying out the pull-in rope. There, it docks with the frame and the pull-in rope is reeled in by the winch on the mobile manipulating device. The conduit is then connected to the subsea structure by the conduit handling mechanism on the frame. The invention also includes the method of attaching a conduit to a subsea structure using the described apparatus.

The present invention is a subsea connection apparatus which can be usedto assist in the subsea connection of flexible or rigid flowlines andumbilicals or bundles (hereinafter referred to as conduits) to subseastructures.

One of the most complex and expensive tasks required to be undertaken bymeans of diverless intervention is that of connecting conduits to subseastructures. In order to make the connection the conduit must bemanoeuvred into position at the subsea structure in a controlled mannerto ensure proper connection of the conduit to the subsea structure. Thisconnection can be made during conduit laying operations by means of avertical connection which uses a surface vessel to position the end ofthe conduit onto a structure connection clamp. In this type ofOn-structure deployment, vertical heave of the vessel can cause damageto the connection points on the subsea structure and conduit; this is aparticular problem in stormy weather. In addition, this techniquerequires the use of a complicated subsea porch structure and anadditional component on the end of the conduit.

Where a conduit is deployed to the seabed with an end termination headat some time prior to connection, the technique is called On-seabedconnection. In such cases, the conduit is pulled to the subsea structureafter deployment on the seabed and the termination head connected to thesubsea structure at a later date with a substantially horizontalconnection. This type of connection is used predominantly in the NorthSea or other offshore environments where the weather conditions areunpredictable. Deployment on soft seabed will result in sinkage of theconduit termination head, an increase in pull-in loads and reducedvisibility. The operation of pulling the termination across the seabedand into the connection position is typically performed by a toolskidmounted onto an ROV. The ROV provides the electrical or hydraulic power,and buoyancy to allow it to support the toolskid and the terminationhead of the conduit.

The conduit may be pulled to subsea structures by docking an ROV andtoolskid onto the conduit termination head then flying the terminationhead to the subsea structure along guide ropes previously connected tothe subsea structure, using a winch and the ROV thrusters. The ROV andtoolskid then dock on the subsea structure and connect the conduit tothe structure.

On-seabed connection becomes very difficult in deep water. Whilst it ispossible to use known, standard ROVs and toolskids up to a depth of 600m, new designs of ROV and toolskid are required for deployment in deepwater because the toolskids must be larger and more powerful, to copewith the increased hydrostatic pressure and higher pull-in and alignmentloads. Furthermore, as depth increases, data transmission becomes slowerand more difficult, and the consequent delay means that operation ROV ismore difficult to control.

The main problems in providing conduit connection are related to eitherguiding the pipeline to the subsea structure or to the resistance of theload that occurs in deep water.

In accordance with the present invention there is provided a subseaconnection apparatus comprising: a frame connectable to a subseastructure; docking means for connecting the frame to the subseastructure; conduit handling means positioned on the frame to facilitatethe positioning of a conduit for attachment to a subsea structure; andmeans for docking a subsea tool and/or vehicle onto the frame.

Preferably, the frame is removably connectable to the subsea structure.

Preferably, the apparatus is further provided with aligning and guidingmeans for aligning a conduit while it is handled by the handling means.

Preferably, the apparatus is further provided with guide means forguiding the apparatus to the subsea structure.

Preferably, the guide means comprises a sleeve having a first end and asecond end, the first end being cylindrical in shape and the second endbeing frustoconical in shape. The sleeve is designed to co-operate withdocking means located on the subsea structure.

Optionally, the apparatus is provided with connection means to which asupport cable is fitted. This supports the weight of the apparatus as itis lowered towards the seabed.

Preferably, the frame has a first end or work area and a second end orhandling area adjacent to the work area.

Preferably, the work area is adapted to allow an ROV to perform aStroke-in operation on a conduit.

Preferably, the apparatus is provided with means to increase itsbuoyancy.

Preferably, the frame is designed to support some or all of themechanical and hydrostatic load associated with connecting a conduit tothe subsea structure.

Preferably, the frame is provided with a latch, the latch beingconnectable to a conduit to allow the conduit to be supported by theframe in a position adjacent to the frame.

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings of which:

FIG. 1 is a perspective view of an embodiment of the present invention;

FIG. 2 a is a perspective view of the embodiment of the presentinvention of FIG. 1 being guided towards a subsea structure, FIG. 2 b isa side view of the present invention being guided towards a subseastructure and FIG. 2 c is a side view of the present invention dockedwith a subsea structure;

FIGS. 3 a to 3 f illustrate the use of the apparatus of the presentinvention for on-seabed conduit connection; and

FIGS. 4 a to 4 f illustrate the use of the apparatus of the presentinvention for catenary pull-in connection.

FIGS. 5 a to 5 d illustrate another embodiment of the subsea connectionapparatus according to the invention. FIGS. 5 a and 5 b are plan viewsof the frame and the termination end of the conduit during alignmentoperations. FIG. 5 c is a side view of an alignment operation. FIG. 5 dis a plan view after the stroke-in of the conduit, i.e. after theconduit has been moved into its final position, ready for clamping tothe subsea structure.

The apparatus of the present invention has been designed for connectionto a subsea structure and is capable of bearing some or all of the loadassociated with connection of a conduit to a subsea structure. In manycases, these loads were previously borne at least in part by an ROVand/or a toolskid. It allows the simplification of the design of the ROVand the toolskid structure so that they can perform connection in deepwater. In preferred embodiments, the apparatus of the present inventionis capable of bearing at least 75% of these loads.

FIG. 1 is a perspective view of the present invention. Details of theframe 5 and the other components of the apparatus will be described withreference to FIG. 1.

FIG. 1 shows the frame 5 which defines a work area 8 arranged, in use,beside the subsea structure 1. The work area 8, is designed to allow anROV with a toolskid to perform a Stroke-in operation on a conduit and tofacilitate clamp operations such as seal replacement, seal areainspection and cleaning, clamp opening and closing, external sealtesting and clamp removal and replacement. Handling area 9 is alsodefined by the frame 5 and is located remote from the subsea structure,in use, and provides access to the area on the subsea structure 1 wherethe termination head of the pipe will be handled.

Situated below the handling area 9 are conduit handling means 10, asshown in FIG. 1. The handling means has two handling members, 10 a, eachhaving an internal surface shaped to receive a conduit. The handlingmembers are connected together by support means 10 b. The docking frame5 can be provided with aligning and guiding means in order to be able toalign the termination head of the conduit, while it is handled by thehandling means, with the connection hub of the subsea structure. Thesemeans allow the guiding of the conduit to a working position where thetermination head is aligned with the subsea structure's connection pointand only a final stroke-in operation has to be performed. These meanscan be actuated by the ROV and its toolskid, most of the loads generatedby this operation shall be transferred directly to frame 5. Interfaces14, as shown in FIG. 1 are incorporated in the frame 5 to provide meansfor docking the toolskid on the frame. The interfaces 14 of the framealso co-operate with docking pins (not shown) of a toolskid which can beconnected to the frame 5 to pull a conduit to the subsea structure'sconnection point or to perform a stroke-in operation.

FIG. 1 shows the frame 5 located on a subsea structure above aconnection point which is located below the central actuation means 12.The connection point is provided with a clamp 3 that contains a centralactuation mechanism 12 and a horizontal leadscrew which allows for avery narrow clamp width of the subsea connection clamp 3.

In addition, the embodiment of FIG. 1 shows a frame 5 which is providedwith docking means to allow it to be removably connected to the subseastructure 1. In addition, in this example, the docking means of theframe contains guide means in the form of a docking sleeve 6 which isconnectable to a guide pin 7 located upon the subsea structure. Theguide pin 7 has a frustoconical end 8 which co-operates with the firstend 18 of the docking sleeve 6 to connect with the guide pin.

The guide pin 7 is also provided with pins 13 which co-operate withslots in the side of the docking sleeve 6 to ensure the correctorientation of the frame 5 with respect to the subsea structure. Thedocking frame 5 may be deployed from the surface on a centralised guidecable 19 extending from a vessel on the surface through the sleeve 6 tothe guide pin 7 on the subsea structure 1 for engagement with the guidepin 7.

FIGS. 2 a–2 c show the apparatus of the present invention being loweredonto the guide pin 7 situated on the subsea structure. Thefrusto-conical first end 18 of the sleeve 6 provides a larger area intowhich the frusto-conical end 8 of the guide pin 7 can be inserted. Thismakes it easier to connect the apparatus to the subsea structure. Theinterconnection of the guide pins with secondary grooves 110 in thesleeve ensure that the apparatus is correctly orientated with respect tothe subsea structure.

In addition, the frame 5 may be provided with connection means 121 towhich a support cable 122 can be attached FIG. 2 b. This providessupport to the apparatus as it is lowered towards the seabed and isparticularly useful in cases where the additional weight of the conduittermination head is contained in the handling means 10 when theapparatus and the termination head are being guided to the subseastructure from the vessel as shown in FIGS. 2 a–2 c. When the conduitand frame are deployed simultaneously, the conduit is in a workingposition so that an ROV and toolskid can perform the stroke-inoperation. The frame with the conduit can be docked on the subseastructure using guide lines deployed from the vessel with the help of anROV, if necessary.

The subsea connection apparatus can be deployed separately from thesubsea structure. Separate deployment is particularly appropriate wherethere are size or weight limitations that preclude deployment of theframe and subsea structure together. The apparatus could be deployed onguide cables as described above or using an ROV to push the frame intothe correct position for docking on the subsea structure.

Further alternatively, the docking frame could be installed by deployingthe docking frame to the seabed in a basket from where it can be pickedup by an ROV and installed on a seabed structure. In this caseadditional ROV Buoyancy may be required to enable the ROV to lift theframe or buoyancy tanks may be incorporated in the apparatus itself. Inaddition, smaller guide pins may be used where the frame is installed byROV.

Typically, on seabed connection (FIGS. 3 a to 3 f) can be achieved usingthe apparatus by flying an ROV containing a toolskid 20, connectingpull-in rope 22 to the termination head of a conduit, docking the ROVand its toolskid 20 on the frame 5 and pulling the conduit to the frameusing a pull-in module, aligning and guiding the conduit to its workingposition using the pull-in module and connecting the conduit to a subseaconnection using a stroke-in module. During the pull-in and stroke-inphased of the operation, the frame bears most of the weight (typically75%) associated with the operation.

In addition, the ROV can perform the pull-in operation and leave thetermination head connected to the frame by means of a hang-off latch andthe stroke-in operation can be performed separately.

In the case of the conduit to be connected during laying operation, theconduit or termination head may be suspended above the seabed. The ROVand its tool skid connects a cable to the termination head of theconduit, and then docks on the frame from where the termination head ispulled to a position below the frame using the pull-in module of thetoolskid and is then connected to the subsea structure using thestroke-in module during the pipe laying operation.

FIGS. 5 a to 5 d show in detail a subsea connection apparatus accordingto the present invention. In particular these figures show in detail theconduit handling means and the guiding and aligning means for aligningthe conduit while it is being handled by the handling means. The frame105 comprises two pivotable outer slide boxes (106 a, 106 b) foraccommodating angular displacement and a front section 109. These slideboxes are pivotable with respect to front section 109. Cylinders areprovided which control the stroke-in distance, the lateral lineardisplacement and the angular displacement of the slide boxes and ensurethe alignment of the conduit in the horizontal plane and a favourableposition of the handling frame as illustrated in FIGS. 5 a and 5 b. Theouter slide boxes support a conduit handling swivelling frame 107 whichhandles the termination end of the conduit. A swivel connection 108 withcontrol cylinders 111 allows pivotable movement between the handlingframe and each outer slide box and ensures the alignment in the verticalplane as illustrated in FIG. 5 c. The subsea connection apparatus can bedeployed onto the subsea structure using frame docking means asillustrated in the embodiment of FIGS. 2 a–2 c. The front frame section109 is linked to the guide sleeve and vertical cylinders can be providedon this part to allow the front frame to move vertically relative to thesubsea structure. The cylinders of the handling means, of the guidingmeans and of the aligning means may be actuated by a ROV docked on thefront frame section 109.

It is important to note that the apparatus is able to be used for onseabed connection (FIGS. 3 a–3 f) for on-structure connection (FIGS. 2a–2 c) or for catenary pull-in connection (FIGS. 4 a–4 f).

By transferring most of the operational loads to the apparatus of thepresent invention, it is possible to use standard ROVs and toolskids fordeepwater conduit connection and it is possible to reduce the size ofROV and toolskid used for deep water applications.

Improvements and modifications may be incorporated herein withoutdeviating from the scope of the invention.

1. A subsea connecting apparatus for connecting a conduit to a subseastructure, the apparatus comprising: a frame connectable to the subseastructure; a first docking mechanism for connecting the frame to thesubsea structure; a conduit handling mechanism on the frame tofacilitate the positioning of a conduit for attachment to the subseastructure; and a second docking mechanism for releasably docking asubsea tool or vehicle onto the frame, whereby the subsea tool orvehicle, after being docked onto the frame, is operable to deliver theconduit to a position at which it is engageable by the frame, whereinthe frame is constructed and configured to engage with the conduit in anoperative relationship after the conduit has been delivered by thesubsea tool or vehicle.
 2. The apparatus as claimed in claim 1, whereinthe frame is removably connectable to the subsea structure.
 3. Theapparatus as claimed in claim 1, wherein the frame further includes analigning and guiding mechanism for aligning a conduit while it ishandled by the handling mechanism.
 4. The apparatus as claimed in claim1, further including a guide mechanism for guiding the apparatus to thesubsea structure.
 5. The apparatus as claimed in claim 4, wherein theguide mechanism comprises a sleeve having a first end and a second end,the first end being cylindrical in shape and the second end beingfrustoconical in shape.
 6. The apparatus as claimed in claim 5, whereinthe guide mechanism is located on the frame, and is constructed tointeract with a complementary guide pin on the subsea structure to formthe docking mechanism.
 7. The apparatus as claimed in claim 6, furtherincluding a guide cable extending from the guide pin to a surfacevessel, the guide mechanism on the frame being movable along the guidecable as it is lowered for docking onto the subsea structure.
 8. Theapparatus as claimed in claim 1, further including a connectionmechanism to which a support cable is connectable.
 9. The apparatus asclaimed in claim 1, wherein the frame has a first end comprising a workarea and a second end or comprising a handling area adjacent to the workarea.
 10. The apparatus as claimed in claim 9, wherein the work area isadapted to allow a subsea vehicle comprising an ROV to perform astroke-in operation on the conduit.
 11. The apparatus as claimed inclaim 1, further including mechanism to increase the buoyancy of theapparatus.
 12. The apparatus as claimed in claim 1, wherein the frameincludes a latch, the latch being connectable to a conduit to allow theconduit to be supported by the frame in a position adjacent to theframe.
 13. A method for connecting a conduit to a subsea structure, themethod comprising the steps of: docking a frame to the subsea structure;operating a connecting mechanism on a subsea tool or vehicle to engagethe conduit for transportation; operating the subsea tool or vehicle totravel to the subsea structure without interaction with the frame;docking the subsea tool or vehicle onto the frame; operating the dockedsubsea tool or vehicle to bring the conduit into an operativerelationship with a conduit handling mechanism on the frame tofacilitate the positioning of the conduit for attachment to the subseastructure; and operating the conduit handling mechanism to couple theconduit to the subsea structure, whereby the frame bears most of theload associated with the operations of the docked subsea tool or vehicleand the conduit handling mechanism, wherein the frame is constructed andconfigured to engage with the conduit in an operative relationship afterthe conduit has been delivered by the subsea tool or vehicle.
 14. Themethod as claimed in claim 13, wherein the step of docking the frame tothe subsea structure includes lowering the frame to the subsea structurealong a guide cable extending from a surface vehicle to the subseastructure and engaging a sleeve on the frame with a complementary pin onthe subsea structure.
 15. The method as claimed in claim 13, wherein thestep of operating the subsea tool or vehicle to travel to the subseastructure comprises paying out a pull-in rope while the subsea tool orvehicle travels under its own power toward the frame; and the step ofbringing the conduit into an operative relationship with the conduithandling mechanism comprises reeling in the pull-in rope after thesubsea tool or vehicle has been docked with the frame.
 16. A subseaconnecting apparatus for connecting a conduit to a subsea structurecomprising: a frame connectable to the subsea structure; a first dockingmechanism for connecting the frame to the subsea structure; a conduithandling mechanism on the frame to facilitate the positioning of aconduit for attachment to the subsea structure; a subsea tool or vehicleincluding a connecting mechanism operable to connect to the conduit fortransportation to the frame, wherein the subsea tool or vehicle isoperable to travel from a location at which it connects to the conduitto the frame under its own power without interaction with the frame orthe subsea structure; a second docking mechanism for releasably dockingthe subsea tool or vehicle onto the frame, wherein: the subsea tool orvehicle is operable when docked to bring the conduit into an operativerelationship with the conduit handling mechanism after the conduit hasbeen delivered by the subsea tool or vehicle; and the frame isconstructed and configured to bear most of the load associated with theoperations of the docked subsea tool or vehicle and the conduit handlingdevice.
 17. The apparatus as claimed in claim 16, wherein the guidemechanism is located on the frame, and is constructed to interact with acomplementary guide pin on the subsea structure to form the dockingmechanism.
 18. The apparatus as claimed in claim 16, further including aguide cable extending from the guide pin to a surface vessel, the guidemechanism on the frame being movable along the guide cable as it islowered for docking onto the subsea structure.
 19. The apparatus asclaimed in claim 16, wherein the first docking mechanism includes aguide cable extending from a surface vehicle to a pin on the subseastructure, and a sleeve on the frame which travels on the guide cableand engages with the pin.
 20. The apparatus as claimed in claim 16,wherein the subsea tool or vehicle comprises a pull-in rope attached toa winch, the winch being operable to pay out the pull-in rope as thesubsea tool or vehicle travels toward the frame.